1. Field of the Invention
This invention relates to a novel method for forming a fluorescent screen of a color cathode ray tube and more particularly to a novel method for forming fluorescent screen having phosphor elements with good adhesion and position to produce a good color picture.
2. Disclosure of Prior Art
A commercial color picture tube for color television receiving, or a color kinescope as it is sometimes called, is a cathode ray tube which includes a viewing screen generally comprised of a multiplicity of red-emitting, green-emitting and blue-emitting phosphor elements of the primary colors. These elements are usually arranged on the screen of a faceplate panel of the tube in a regular cycle array. In a color cathode ray tube having a color selecting mask, the phosphor elements are usually dots, continual strip pieces or continuous strip pieces arranged in groups of threes or triads. Each triad is associated with a particular perforated aperture in the color selecting mask (also called mask).
Recently, it is getting more popular that the color cathode ray tube have a screen comprising a light absorbing matrix lying in the space between the phosphor elements.
Depositing the multiplicity of phosphor elements on the screen of the color cathode ray tube presents difficult problems of fabrication. One useful processing technique contemplates that the entire screen area is covered with the phosphor of one of the primary colors and a photosensitive resist. After the screen has been coated with such materials, it is placed in so-called "lighthouse" in which a high intensity light exposes the screen through the mask that ultimately is assembled with the screen in the completed tube. By positioning the light source to simulate the action of an electron gun associated with the phosphor being processed, an exposure pattern results which corresponds to the desired location of the elements of the phosphor being processed. After exposure, the screen may be developed (washing) to remove unexposed portion of the coating and leave as a residue the phosphor elements of one of the primary colors.
Repetition of the same general process permits depositing elements of the other phosphors although it will be understood that the coating in each step of the process includes a phosphor of a given color and its exposure in the lighthouse is with a light source properly positioned to simulate the electron gun assigned to that color.
This processing can be satisfactorily employed except that there are certain difficult problems in the adhesion of the elements to the faceplate panel of the tube. If the exposure is extended, this adhesion will be increased but an undesired enlargement of certain of the phosphor elements will be effected.
In the process for forming the light absorbing matrix on the faceplate panel, difficult problems equivalent to that of the phosphor elements occur in preparing removable elements made usually of photosensitive material in which the removable elements are available to provide holes in the light absorbing matrix. In other words, the removable elements are required to be the same as the phosphor elements to be formed, because the holes in the light absorbing matrix determine the size and position of the effective phosphor elements of a completed fluorescent screen of the tube.
Another exposure process technique so-called "back exposure" has been proposed. In this "back exposure" technique, as heretofore carried out, the screen is also exposed from the side of the faceplate panel opposite to that side which bears the screening coating. As the back exposure increases, to some extent, the effect of the forward exposure through the mask, it may overcome the problems of the poor adhesion raised in the forward exposure but it may also introduce an undesired phosphor depositing on the screen area of a certain phosphor element which will be deposited thereafter, consequently the color purity of the phosphor elements deteriorates. This added back exposure may further cause an undesired enlargement of certain phosphor elements. Thus, this back exposure technique has been impractical.
Accordingly, it is an object of the invention to provide a novel method for forming a fluorescent screen of a color cathode ray tube which avoids the aforementioned problems of the prior art.
It is other object of the invention to provide a novel method for preparing a light absorbing matrix with desired holes.